All About Titanium Alloy 6-4: Definition, History, Properties, and Applications
Titanium alloys are highly significant in modern engineering due to their exceptional blend of properties such as strength, low density, and corrosion resistance. Among these alloys, titanium alloy 6-4, also known as grade 5 titanium alloy, Ti-6Al-4V, or 6Al-4V titanium, stands out as one of the most versatile titanium alloys. Additionally, titanium alloy 6-4 is the most commonly used titanium alloy and accounts for nearly half of all titanium used in the world. From use in automotive parts like exhausts and springs to medical components like joint implants, 6Al-4V titanium is used in a broad range of applications across many different industries.
This article will review titanium alloy 6-4, its definition, history, its properties, and different applications.
What Is Titanium Alloy 6-4?
Titanium alloy 6-4, or grade 5 titanium, with its unique set of properties, is a remarkable alloy that is deemed the workhorse alloy of the titanium industry. Titanium 6-4, also known as Ti-6Al-4V alloy, is an alpha-beta titanium alloy in which aluminum acts as the alpha stabilizer and vanadium acts as the beta stabilizer. Ti-6Al-4V composition is 5.5–6.75% aluminum and 3.5–4.5% vanadium, with the remaining percentage being titanium. Titanium alloy 6-4 offers a great blend of high strength and stiffness, corrosion resistance, and low density. This makes it great for applications in which these properties are required such as: in the aerospace, automotive, or medical industries. Its use in these industries, as well as others, has led to a host of new products that are lighter, more efficient, and safer.
Who Is the Inventor of Titanium Alloy 6-4?
Titanium alloy 6-4 was invented by metallurgist and MIT professor Stan Abkowitz in 1951 at the Watertown Arsenal Laboratory, a facility of the US Army. It was invented by adding molten aluminum and vanadium to molten, pure titanium. The alloy’s first widespread use was for the production of the US military’s U2 high-altitude reconnaissance plane in the 1950s. The invention of the alloy and its use in the production of this aircraft catalyzed the titanium industry. Today, Ti-6Al-4V is the most commonly used titanium alloy in the world.
How Is Ti-6AL-4V Made?
The production of Ti-6Al-4V starts with the Kroll Process. The Kroll process is the most commonly used method to produce commercially pure titanium. In this process, titanium-rich ores such as ilmenite or rutile are heated to produce liquid titanium tetrachloride (TiCl4). Through a fractional distillation process similar to producing gasoline from crude oil, the TiCl4 liquid is purified. Afterward, magnesium is added to the liquid to produce a sponge-like titanium material and a magnesium-based salt. Next, the sponge is compressed and melted. At this stage, the appropriate ratio of aluminum and vanadium is added to the molten titanium. Once added, the Ti-6Al-4V alloy is cast into ingots and other shapes.
What Are the Properties of Titanium Alloy 6-4?
Titanium alloy 6-4 has many desirable properties that make it great for use in various applications. The different properties of titanium alloy 6-4 are listed below:
1. Low Thermal Conductivity
Titanium 6-4 has a low thermal conductivity of 6.7 W/mK. Its low thermal conductivity means the titanium alloy can be used in a broad temperature range without its mechanical properties being affected. This makes the alloy great for high-heat applications such as jet engines and landing gear in aircraft, exhaust systems in automobiles, and chemical processing equipment.
2. Shear Mechanism
6Al-4V Ti has low shear strength between 550–760 MPa compared to other commonly used metals like steel or aluminum. It is unsuitable for applications in which high shear forces are likely to be applied.
3. High Tensile Strength
Titanium 6-4 has an exceptional tensile strength of 1,170 MPa. Its high tensile strength, coupled with its low density of 4.43 g/cm3 makes it an excellent material for applications in which high strength but light weight are desired—particularly in the automotive, aerospace, and medical industries. For more information, see our guide on Material Tensile Strength.
4. High Modulus of Elasticity
Ti-6Al-4V has a high elastic modulus of 114 GPa. Its high modulus of elasticity means the material is stiff, rigid, and resistant to deformation. Consequently, the stiffness of 6Al-4V titanium alloy helps to minimize the deformation or bending of critical parts and acts as a vibration damper to reduce the risk of fatigue failure.
What Are the Physical Properties of Titanium Alloy 6-4?
Some physical properties of titanium alloy 6-4 are described in Table 1 below:
| Physical Property | Value |
|---|---|
Physical Property Density | Value 4.43 g/cm3 (0.16 lb/in^3) |
Physical Property Hardness | Value 379 HB (41 HRC) |
Physical Property Melting Temperature | Value 1,604–1,660 °C (2,920–3,020 °F) |
Physical Property Specific Heat Capacity | Value 0.5263 J/g°C (0.126 BTU/lb°F) |
Physical Property Thermal Conductivity | Value 6.7 W/mK (46.5 BTU*in/hr-ft2-°F) |
Physical Property Electrical Resistivity | Value 0.000178 Ωcm |
| Mechanical Property | Value |
|---|---|
Mechanical Property Yield Strength | Value 1,100 MPa (160 ksi) |
Mechanical Property Ultimate Tensile Strength | Value 1,170 MPa (170 ksi) |
Mechanical Property Modulus of Elasticity | Value 114 GPa (16,500 ksi) |
Mechanical Property Shear Strength | Value 760 MPa (110 ksi) |
Mechanical Property Shear Modulus | Value 44 GPa (6,380 ksi) |
Mechanical Property Poisson’s Ratio | Value 0.33 |
What Are the Applications of Ti6Al4V?
Ti6Al4V has many desirable properties that make it preferred for many applications across different industries such as:
1. Chemical Industry
Corrosion resistance and strength are two properties essential to a properly functioning and safe chemical processing system. Titanium alloy 6-4 has numerous uses within the chemical industry since it exhibits both these properties and, consequently, reduces maintenance costs and extends the life of chemical equipment. Pressure vessels, heat exchangers, tank agitators, and piping systems are common applications of the alloy in the chemical industry.
2. Medical Industry
The medical industry requires parts and components to be made of exceptional quality and tight tolerances for effective, safe, and comfortable use. Titanium 6-4 is often used in the medical industry due to its high strength, low weight, corrosion resistance, and biocompatibility. Orthopedic and dental implants, surgical instruments, and prostheses are some examples of medical parts commonly fabricated from 6Al-4V titanium.
3. Additive Manufacturing
Additive manufacturing, also known as 3D printing, is the manufacturing process of creating three-dimensional parts layer-by-layer until the entire object is created. There are many different types of 3D printing, however, each type involves the fusing of subsequent layers to create a rigid part. Each layer of a 3D-printed part is a thin slice of the cross-section of the entire part. Ti-6Al-4V is compatible with additive manufacturing through powder bed fusion methods like selective laser melting (SLM), direct metal laser sintering (DMLS), or electron beam melting (EBM). 3D printing of Ti-6Al-4V parts is great for rapid prototyping to verify part form and function and for the mass production of complex parts in different industries such as: automotive, aerospace, and power generation industries.
4. Marine Industry Applications
Two of the most critical material properties in marine applications are corrosion resistance and strength. Ti-6Al-4V alloy is suitable for many marine applications since it has high strength and exhibits great corrosion resistance in seawater. Marine applications of the grade 5 alloy include: onboard tanks, piping, bulkheads, hatches, and propulsion systems.
5. Gas Turbines
6Al-4V titanium alloy is a great material choice for gas turbines used in the aerospace and petroleum industries. The material is a good choice for these applications due to its strength, corrosion resistance, and suitability for a wide operating temperature range. Consequently, titanium 6Al-4V provides reliability, reduced maintenance, and a long-term life for gas turbine assemblies.
6. Firearm Suppressors
Another common use of grade 5 titanium is in firearm suppressors. Compared to other metals commonly used for firearm suppressors, particularly stainless steel, Ti-6Al-4V is lighter, has a higher strength-to-weight ratio, and a lower thermal conductivity than steel. The material’s low density and high strength-to-weight ratio mean the weapon will be lighter, but still be able to handle the forces experienced when in use. Additionally, since Ti-6Al-4V has a lower thermal conductivity, the effects of heat are not as severe compared to stainless steel suppressors.
7. Aerospace Industry
The aerospace industry is one of the largest utilizers of titanium 6-4 alloys. Weight and high strength are both critical elements to aircraft performance and efficiency. Ti-6Al-4V is ideal for the aerospace industry due to its lightweight, high strength, corrosion resistance, and ability to be used in a wide operating temperature range. 6Al-4V titanium is used in the aerospace industry for parts like: aircraft frames, landing gear components, fuselage components, and engine parts.
8. Power Generation Industry
The power generation industry is another industry that commonly employs titanium alloy 6-4 in various parts, components, and assemblies. In the power generation industry, materials with high strength and corrosion resistance, as well as materials capable of being used in a wide operating temperature range are highly desired. Titanium 6-4 checks all three of those boxes. From heat exchanger tubings and condensers to turbine blades, Ti-6Al-4V is great for use in the power generation industry.
What Are the Advantages of Ti-6Al-4V?
There are many advantages of Ti6Al4V alloy that make it great for various applications in different industries, such as:
- Has a high strength-to-weight ratio, with a tensile strength of 1,170 MPa and a density of only 4.43 g/cm3. This ratio makes the material indispensable in aerospace, automotive, and other weight-sensitive applications, as it improves product efficiency and performance.
- Is naturally corrosion resistant due to the oxide layer that forms on the material’s surface.
- Is biocompatible and does not react in the human body.
- Can endure repeated stress cycles without failure. This extends its life span in demanding applications, particularly in the aerospace and oil & gas industries.
What Are the Disadvantages of Ti-6Al-4V?
The disadvantages of Ti6Al4V are listed and described below:
- Titanium alloys are expensive, and Ti-6Al-4V is no different. The process of refining pure titanium and subsequently producing titanium alloys is extensive and requires sophisticated machinery.
- Notoriously hard to machine, which can increase manufacturing costs. This is because titanium has a low thermal conductivity which causes heat to build in the cutting tool, rather than in the workpiece.
- Welding Ti-6Al-4V can be challenging and may require specialized equipment and techniques.
- Has poor shear strength and surface-wear properties. Consequently, the material has a tendency to seize or slip when in contact with sliding parts.
- While Ti-6Al-4V is generally very corrosion resistant, it is not corrosion resistant against strong acids like hydrochloric or sulfuric acids. These materials cause the protective oxide layer on the material to break down upon contact.
What Is the Tensile Strength of Ti-6Al-4V?
The tensile strength of Ti-6Al-4V is 1,170 MPa or 170 ksi. The tensile strength of Ti-6Al-4V is determined by conducting a tensile test. In a tensile test, a test specimen is subjected to an increasing tensile load until the specimen ruptures. A stress-strain curve shows the stress applied to the part on the Y-axis and the strain of the part on the X-axis. The stress value at the point of rupture is considered the tensile strength of the material.
What Is the Hardness of Ti-6Al-4V?
Ti-6Al-4V alloy has a hardness of 379 HB and 41 HRC.
What Is the Density of Ti-6Al-4V?
The density of Ti-6Al-4V alloy is 4.43 g/cm3. As a comparison, the approximate density of stainless steel is 8 g/cm3—almost double the value of Ti-6Al-4V.
What Is the Melting Point of Ti-6Al-4V?
The melting point of Ti-6Al-4V alloy is between 1,604–1,660 °C.
How Much Does Ti-6Al-4V Cost?
The cost of Ti-6Al-4V alloy can vary significantly depending on factors such as purity, form (e.g., sheet, bar, or powder), and production techniques. Generally, titanium alloys are more expensive than other common metals like steel or aluminum due to the energy-intensive extraction and processing of titanium ores. For instance, a 1” diameter, 6’-long titanium 6-4 alloy bar costs roughly $775—with the cost drastically increasing with larger diameters or longer lengths. When it comes to 3D printing, titanium 6-4 powder can cost up to $429 per kilogram of material.
Is Titanium Alloy 6-4 Magnetic?
No, titanium alloy 6-4 is not magnetic. None of the commercially pure titanium and titanium alloys in the market are magnetic.
Summary
This article presented titanium alloy 6-4, explained it, and discussed its properties and various applications. To learn more about titanium alloy 6-4, contact a Xometry representative.
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